1. Field of the Invention
The present invention relates to an image capture apparatus and a method of controlling the same.
2. Description of the Related Art
Conventionally, video cameras and still cameras have differed in many respects. The former apparatuses have been apparatuses designed to capture only moving images, whereas the latter apparatuses have been apparatuses designed to capture only still images. However, both the types of apparatuses have started using image sensors and have digitally processed images. This has been reducing the differences between them. Recently, the still image shooting function of a video camera and the movie shooting function of a still camera have greatly advanced from the initial levels to such an extent that even a compact still camera like that built in a cellular phone can perform movie shooting with a full HD (high definition) resolution.
Recently, in particular, since a digital still camera with interchangeable lenses has also been equipped with a movie shooting function, movie shooting by the still camera has attracted a great deal of attention. This may be because a digital still camera with interchangeable lenses uses a large-sized image sensor with a large number of pixels, interchanging lenses facilitates changing the angle of view, and allows still image shooting with high image quality.
When performing shooting operation premised on being subjected to editing as in the case of movies and television, the apparatus performs recording with importance being attached to tone gradation to minimize blown-out highlights and blocked-up shadows so as to ensure an adjustable range at the time of editing. More specifically, it is known that recording is performed by using nonlinear input-output characteristics that exhibit a logarithmic increase with an increase in luminance value. Such nonlinear input-output characteristics are called Log or Log gamma and defined as a function or table. In addition, further converting film scan data, converted by the defined Log gamma, by using Cineon LOG or the like proposed for film scan data recording proposed by Kodak, U.S.A. allows the data to be handled as image data similar in characteristic to the photosensitivity of a photograph film. Using Log gamma can maintain high tone gradation by suppressing blown-out highlights and blocked-up shadows. However, the recorded moving image becomes a low-contrast image, with a dark portion becoming brighter and a bright portion becoming darker. For this reason, this image is not suitable for appreciation without any change, and hence needs to be converted into linear tone characteristics with respect to human visual features in the end.
In television or movie production, moving images having Log gamma characteristics are generally edited. Conventionally, however, the movie shooting function of a digital still camera is designed to record moving images having tone characteristics or contrast suitable for appreciation without any editing processing after shooting operation (to be referred to as postproduction processing). For this reason, digital still cameras have also been required to support movie recording using Log gamma.
In an image signal, a color space to be filled is specified in accordance with specifications. For example, such a color space is specified by JPEG generally used for still images or the ITU-R (International Telecommunication Unit-Radio) BT.601 specification for SD (Standard Definition) television and video signals (Recommendation ITU-R BT.601-7 (March 2011) Studio encoding parameters of digital television for standard 4:3 and wide-screen 16:9 aspect ratios [retrieved Apr. 9, 2012], Internet <URL: http://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.601-7-201103-I!!PDF-E.pdf>). As for HD (High Definition) television and video signals, the ITU-R BT.709 specification specifies such a color space (Recommendation ITU-R BT.709-5 (April 2002) Parameter values for the HDTV standards for production and international programme exchange [retrieved Apr. 9, 2012], Internet <URL: http://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.709-5-200204-I!!PDF-E.pdf>).
In addition, still image recording uses the color space specified by the BT.601 specification (to be simply referred to as the BT.601 color space hereinafter), and hence internal processing in a digital still camera is generally premised on an image signal in the BT.601 color space. At the time of HD movie shooting, the apparatus processes an image signal in the BT.601 color space and converts the signal into a signal in the BT.709 color space before recording or external output operation. This is because when the apparatus performs still image shooting during movie shooting (or still image generation from a moving image), it is necessary to match the color of the still image with that of the moving image. In this case, the color spaces specified by the BT.601 and BT.709 specifications aim at RGB to YUV color conversion matrix coefficients defined by the respective specifications but do not aim at primary (gamut) or gamma based on color specifications.
However, since color space conversion is computation processing, repeated computation processing may cause image quality degradation due to computation errors. For this reason, the smaller the number of times of application of color space conversion, the better. However, upon processing HD movie shooting using Log gamma like conventional movie shooting, the apparatus performs color signal processing or luminance signal processing after conversion to a signal in the BT.601 color space, and then converts the signal into a signal in the BT.709 color space at the time of recording. In this case, the apparatus applies color space conversion processing to an image signal at least twice in the interval between the instant the signal is output from the image sensor and the instant the signal is recorded.